Wetting Dynamics of Nanoparticle Dispersions: From Fully Spreading to Non-sticking and the Deposition of Nanoparticle-Laden Surface Droplets

Early Time Spreading Dynamics of Nanobubble-Laden Drops

Nanobubbles, when dispersed in a liquid phase, may enhance mass transport, adsorption, and reactions in many industrial applications, such as fabrication of functional materials, drug delivery, water treatment, carbon dioxide capture, and surface decontamination. Here, we experimentally study the early time spreading dynamics of nanobubble-laden surfactant drops on a hydrophilic solid surface submerged in an oil phase. Along with recovering the retarding effects of surfactants on the early time wetting dynamics, we report that nanobubbles can weaken Marangoni stresses and consequently reduce the duration of the retardation regime. Remarkably, we find that the duration of this retardation regime (tr) exponentially decays with the nanobubble concentration in the dispersion (Nb) according to Nb ∼ log(1/tr). The micro-particle imaging velocimetry analysis of the flow field inside the drop indicates a large reduction in the magnitude of velocities in the presence of surface-active materials, confirming the existence of Marangoni flow that opposes droplet spreading. Our research introduces a simple approach to calculate the nanobubble concentrations in liquids and offers guidelines for controlling wetting dynamics.

Structural and dynamical equilibrium properties of hard board-like particles in parallel confinement

We performed Monte Carlo and dynamic Monte Carlo simulations to model the diffusion of monodispersed suspensions composed of impenetrable cuboidal particles, specifically hard board-like particles (HBPs), in the presence of parallel hard walls. The impact of the walls was investigated by adjusting the size of the simulation box while maintaining constant packing fractions, fixed at η = 0.150, for systems consisting of HBPs with prolate, dual-shaped, and oblate geometries. We observed that increasing the distance between the walls led to the recovery of an isotropic bulk phase, while local particle organization near the walls remained stable. Due to their shape, oblate HBPs exhibit more efficient anchoring at wall surfaces compared to prolate shapes. The formation of nematic-like particle assemblies near the walls, confirmed by theoretical calculations based on density functional theory, significantly influenced local particle dynamics. This effect was particularly pronounced to the extent that a modest portion of cuboids near the walls tended to diffuse exclusively in planes parallel to the confinement, even more efficiently than observed in the bulk regions.